test: add test that fails with gofrontend

The gofrontend code doesn't correctly handle inlining a function that
refers to a constant with methods.

For #35739

Change-Id: I6bd0b5cd4272dbe9969634b4821e668acacfdcf9
Reviewed-on: https://go-review.googlesource.com/c/go/+/261662
Trust: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>

test/fixedbugs/issue35739.dir/a.go

@@ -0,0 +1,15 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package a
+
+type myError string
+
+func (e myError) Error() string { return string(e) }
+
+const myErrorVal myError = "error"
+
+func IsMyError(err error) bool {
+	return err == error(myErrorVal)
+}

test/fixedbugs/issue35739.dir/b.go

@@ -0,0 +1,11 @@
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package b
+
+import "./a"
+
+func F(err error) bool {
+	return a.IsMyError(err)
+}

test/fixedbugs/issue35739.go

@@ -0,0 +1,9 @@
+// compiledir
+
+// Copyright 2020 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 35739: gccgo inlining error with constant with method.
+
+package ignored